During the last decade pure analog circuit as well as mixed signal circuits were integrated with digital circuits.
Various modern system on chip (SoC) integrated circuits as well as other types of integrated circuits include analog circuits. Analog circuits are much more sensitive to noise than digital circuits. In many cases the digital circuit generates a noise signal that can disrupt the operation of analog circuits. At least some of the noise signals propagate along the power supply conductors.
U.S. Pat. No. 6,286,117 of Yun et al., being incorporated herein by reference, describes a circuit and method that provide a noisy output signal to a logic device.
U.S. patent application publication serial number 2004/0104732 of Oosawa et al., being incorporated herein by reference, describes a method and device for switching between signals provided by a digital test circuit (that tests a digital test circuit) and between signals provided by an analog circuit.
In order to reduce the noise that is received by the analog circuit many modern integrated circuits feed the analog circuit with a supply voltage provided by an internal power supply module. The internal power supply module usually receives a stable reference signal and a non-stable high level voltage supply and outputs a more stabilized supply voltage to the analog circuit.
Nevertheless, even when an internal power supply module is used, a certain amount of noise may be induced by surrounding digital circuits and still reaches the analog circuit.
Merely providing a noisy high-level voltage supply to the internal power supply module (via an input of the integrated circuit) does not test the noise immunity characteristics of the analog circuit but rather provides an indication about supply noise rejection ratio of the internal power supply.
There is a need to provide an efficient method and device for testing one or more noise immunity characteristics of an analog circuit within an integrated circuit.